The invention relates to a field effect transistor memory cell having a source region, a drain region, a channel region and a gate region, with the channel region extending from the source region to the drain region and being formed by at least one nanowire. Furthermore, the invention relates to a semiconductor memory device which comprises a plurality of such field effect transistor memory cells and to a method of manufacturing such a memory cell or a plurality of memory cells which can be connected together to form a semiconductor memory device or are connected together to form a semiconductor memory device.
A field effect transistor (FET) of which the source, channel and drain regions are formed by a nanowire and the gate region of which is formed by a nano tube is known from WO 02/03482 A1. A storage of electrical charges is not provided for in this FET.
A memory structure in which electrical charges can be stored in silicon nano-crystals with a size of approximately 5 nm is described in the article by S. Tiwari et al., Appl. Phys. Lett. 68 (10), pages 1377–1379 (1996). The memory structure is based on a silicon field effect transistor in which the entire channel region is covered by a layer of silicon nanocrystals, with this nanocrystal layer being separated by a thin tunnel oxide from the channel region and by a thicker tunnel oxide from the gate region.
A “floating gate” MOSFET is known from the article by P. Normand, Mat. Sci. Eng. C 15, pages 145–147 (2001) in which silicon nanocrystals are used as charge storage elements and are embedded in the gate oxide.
A logic circuit is described in the article by A. Bachtold, Science 294, pages 1317–1320 (2001) which is formed from a plurality of field effect transistors on the basis of single walled carbon nanotubes. The semiconducting nanotubes each form the channel region of a field effect transistor. They are each contacted by two gold electrodes and an aluminium wire which acts as a gate is arranged between them. The aluminium wire is electrically insulated relative to the nanotubes by thin layer of native aluminium oxide.
T. Rueckes et al. describe in Science 289, pages 94–97 (2000) a non-volatile memory with random access (“non-volatile random access memory”) in which a plurality of nanotubes and/or nanowires are arranged transverse to one another. Two crossing nanotubes or nanowires are spaced from one another and the spacing can be changed by the application of a voltage as a result of the attractive electrostatic forces. Because of the interplay of the elastic deformation energy and the attractive van der Waals energy of the nanotubes or -wires two precisely defined states, so-called bistable states, can be set up in this manner. In one state two crossing nanotubes or nanowires are in contact with one another, in the other state they are not in contact with one another. In this arrangement the resistance of the individual nanotubes or nanowires remains largely unchanged. In order to switch over between the two states voltages of up to 40 V are necessary.